Note 2 - Significant Accounting Policies and Methods of Application (Detail) - Summary of Regulatory Assets and Liabilities (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Regulatory assets
Regulatory assets - current	$ 145	$ 131
Regulatory assets - noncurrent	944	1,079
Total regulatory assets	1,089	1,210
Regulatory liabilities
Regulatory liabilities - current	161	112
Regulatory liabilities - noncurrent	1,477	1,405
Total regulatory liabilities	1,638	1,517
Accrued natural gas costs [Member]
Regulatory liabilities
Regulatory liabilities - current	93	53
Bad debt rider [Member]
Regulatory liabilities
Regulatory liabilities - current	37	30
Regulatory liabilities - noncurrent	17	14
Accumulated removal costs [Member]
Regulatory liabilities
Regulatory liabilities - current	16	14
Regulatory liabilities - noncurrent	1,393	1,321
Other Regulatory Liabilities [Member]
Regulatory liabilities
Regulatory liabilities - current	15	15
Regulatory liabilities - noncurrent	11	11
Unamortized investment tax credit [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	29	32
Regulatory income tax liability [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	27	27
Recoverable regulatory infrastructure program costs [Member]
Regulatory assets
Regulatory assets - current	47	48
Regulatory assets - noncurrent	167	305
Recoverable ERC [Member]
Regulatory assets
Regulatory assets - current	38	7
Regulatory assets - noncurrent	438	351
Recoverable Pension And Other Retirement Benefit Costs [Member]
Regulatory assets
Regulatory assets - current	19	29
Regulatory assets - noncurrent	196	262
Other Regulatory Assets [Member]
Regulatory assets
Regulatory assets - current	41	47
Regulatory assets - noncurrent	53	62
Long-Term Debt Fair Value Adjustment [Member]
Regulatory assets
Regulatory assets - noncurrent	$ 90	$ 99